The present invention relates to a continuously operating prepress or finishing press for the manufacture of panels, such as chipboards, fiberboards, or the like, employing two superposed endless plate-link belts rotating about polygonal rolls arranged horizontally and in parallel to each other, each belt consisting of mutually articulated platens provided on their edges extending at right angles to the travel direction of each endless platen belt with recesses and corresponding projections. Adjacent platens are joined together by way of guide arms mounted or supported only in the zone of (i.e. adjacent) the lateral surfaces of the platens approximately in the depth of the recesses of adjacent platens. Each projection is provided at its free end and each recess at its base with respective rabbets. Moreover, each platen supports itself when in the press inlet zone with its rabbet lug in the open rabbets of the trailing platen as seen in the travel direction. At least one of the two endless platen belts is moveable by at least partially driveable pressure rolls subjected to variable pressure forces by means of hydraulic cylinders and optionally also be exerting a driving force on at least one polygonal roll, and each endless platen belt is surrounded by an endless steel belt.
In a conventional press of this type (see German Utility Model No. 7,315,139), bending forces effective on the projections of the platens can be more readily absorbed, the pressure rolls are always in good contact in the zone of the junction points of adjacent platens, the specific contact pressure to be exerted on the platen belts via the pressure rolls is lower than heretofore, the individual platens can be made to be substantially thinner, the adjacent pins are practically not at all stressed via the pins connecting the guide arms, and the peripheral speed of the endless platen belts and the surrounding endless steel belts can be considerably increased without danger of oscillation of the endless platen belts.
Although the endless platen belts of the aforementioned type have proven themselves well, linear impressions are caused in the chip layer to be compressed when the pressure exerted on the pressure rolls is maintained at an essentially constant level, especially if the speed of rotation of the enless platen belts is increased to raise the output speed of the continuously operating press. This is due at least to the trapezoidal and/or triangular projections of the endless platens of the upper endless plate-link chain. Unfortunately, this effect is realized even in spite of the provision of endless steel belts surrounding the endless platen belts. This, of course, is undesirable.